1. Field of the Invention
This invention relates generally to compositions for whitening human teeth, and more particularly, to compositions that do not contain hydrocarbon humectants and which when applied onto the surface of teeth act to whiten without damage to tooth surfaces.
2. The Prior Art
A tooth is comprised of an inner dentin layer and an outer hard enamel layer which is coated with a protective layer called the pellicle. Teeth can become stained when the chromogenic materials penetrate the enamel or chromogenic materials get trapped within the pellicle.
Many substances can stain or reduce the whiteness of one's teeth. In particular, the foods, tobacco products and fluids such as tea and coffee that one consumes tend to stain one's teeth. These products or substances tend to accumulate within the pellicle and then permeate the enamel. This problem occurs gradually over many years, but imparts a noticeable discoloration of the enamel of one's teeth.
Stain can be removed from tooth surfaces by the use of dentifrices, especially toothpaste, gels and powders containing active oxygen or hydrogen peroxide liberating ingredients such as peroxides, percarbonates and perborates of alkali and alkaline earth metals or complex compounds containing hydrogen peroxide with salts of the alkali or alkaline earth metals. However, these methods generally work very slowly and do not fulfill the needs of individuals who desire rapid whitening of teeth.
Individuals desiring rapid whitening of teeth can usually have it done in the dental office. One method for whitening teeth used by dental professionals involves the use of 30-35% hydrogen peroxide in combination with heat and/or light to promote the oxidation reaction. This method, although fast, is losing favor with dentists because clinical and scientific evidence shows that high concentrations of peroxide are deleterious to oral tissues. Improvements to this method have resulted in the usage of lower concentrations of hydrogen peroxide. However, this method also has a drawback because it is expensive and confines the patient to the dental chair for extended periods of time.
Another professional method for bleaching teeth involves the use of hydrogen peroxide generating compounds such as urea peroxide (carbamide peroxide) at concentrations of 10-20% to achieve the desired whitening effect. Urea peroxide rapidly breaks down into hydrogen peroxide due to the water present in saliva. This method known as at home use dentist dispensed bleaching system involves the use of a mouth guard or tray within which the bleaching agent is placed. The tray is then placed upon the teeth of the patient and bleaching is allowed to take place. This method of treatment has drawbacks including tooth sensitivity, possibly due to demineralization and irritation of oral tissues. An additional disadvantage of the tray application method is that the bleaching effect is very slow compared to in-office methods.
One of the drawbacks to home use bleaching products containing oxygen liberating bleaching compounds is the tendency of these products to decompose within a relatively short period of time following manufacture with concomitant loss of all or a substantial amount of the available oxygen thereby limiting the efficacy of these products as teeth whitening compositions. Peroxy compounds such as hydrogen peroxide are notoriously unstable with respect to maintenance of peroxide level and have been found to be difficult to formulate into aqueous gels or pastes which will have an adequate shelf-life and yet will readily liberate oxygen when applied to the oral cavity. Therefore, the prior art, for example U.S. Pat. Nos. 4,988,450 and 3,657,413 in formulating oxygen liberating compositions for the whitening of teeth utilize anhydrous powders or water-free pastes or gels which must be protected against contamination and chemical interaction. A drawback to the use of such anhydrous products is that, due to the absence of water, application of the oral composition tends to desiccate oral tissues which leads to irritation and tissue damage.
In order to overcome the disadvantage of irritation and tissue desiccation, prior art discloses oxygen releasing toothpaste compositions which have greater water content, however all have hydrocarbon humectants or hydrocarbon carriers such as glycerin, sorbitol, polyethylene glycol etc. The purpose of the humectant is to keep the composition from hardening upon exposure to air. Illustrative of oral compositions containing peroxide compounds include U.S. Pat. Nos. 4,980,152; 4,839,156; 4,522,805; 4,567,036; 4,405,599; 4,980,152; 5,171,564; and 5,256,402.
U.S. Pat. No. 4,980,152 discloses a non-abrasive aqueous oral gel composition comprising about 0.5 to about 10% by weight urea peroxide and 0.01 to 2% by weight of a fluoride providing compound. The composition further includes a thickening agent such as carboxy polymethylene, a non-ionic surfactant such as Pluronic F127, alkali soluble cellulose ethers as viscosity increasing agents, potassium phosphate as a buffering agent and glycerin as a carrier and flavoring and sweetening agents.
U.S. Pat. No. 4,839,156 discloses an aqueous dental gel containing 18-25% by weight of a polyoxyethylene polypropylene block copolymer gelling agent, hydrogen peroxide, 15-40% by weight of a polyethylene glycol humectant, flavor, sweetening agent and a non-ionic surfactant as the essential ingredients. This has been defined as a ringing gel, however addition of metal chelating agents have been described to have an adverse impact upon the stability of peroxide.
U.S. Pat. Nos. 4,522,805 and 4,567,036 disclose a stable toothpaste to aid in controlling periodontal disease, containing an oxidizing agent such as urea peroxide which dissociates into urea and hydrogen peroxide in the oral cavity, in a paste carrier comprising an anionic detergent, sorbitol and glycerin humectant and a thickening agent such as gum tragacanth, sodium alginate or sodium carboxymethyl cellulose.
U.S. Pat. No. 4,405,599 discloses toothpaste consisting essentially of a combination of calcium peroxide and sodium perborate oxidizing agents, dicalcium phosphate, calcium carbonate and magnesium carbonate cleaning agents, sorbitol humectant, cornstarch, cellulose gum thickening agents, and an anionic detergent. There is no indication of the effect of the toothpaste on whitening or stain removal from teeth.
U.S. Pat. No. 4,980,152 discloses toothpaste consisting of urea or hydrogen peroxide with a fluoride compound as a pH stabilizing compound. There is no indication of the effect of the toothpaste on whitening or stain removal from teeth.
U.S. Pat. No. 5,171,564 discloses an oral care composition which contains an abrasive in combination with a metal free peroxide, a chelating agent, thickening agent such as a polyoxyethylene polypropylene block copolymer and humectants such as polyethylene glycol, glycerin or sorbitol.
U.S. Pat. No. 5,256,402 discloses an oral care composition which contains an abrasive in combination with a metal free peroxide, a chelating agent, tooth desensitizing agents and thickening agent such as a polyoxyethylene polypropylene block copolymer and humectants such as polyethylene glycol, glycerin or sorbitol.
The prior art listed above, all contain hydrocarbon humectants and have a primary drawback of having limited stain removal/tooth whitening effectiveness. The purpose of the hydrocarbon humectants in tooth whitening compositions is to help solubilize flavor materials, surfactants and also to act as a carrier for peroxides. However, hydrocarbon humectants have a disadvantage because they are known to react with the active bleaching species such as free radicals and the perhydroxyl anions. Other prior art compositions contain abrasives which have been shown to abrade enamel. In addition, newer tooth colored restorative materials contain very fine filler particles in order to increase polishability unfortunately, this has been shown to decrease abrasion resistance. Hence, there is a need for toothbrush applied dentifrice compositions which do not contain hydrocarbon humectants and do not contain abrasives.
Dentist dispensed splint applied compositions are thought to have greater activity because the contact time between the tooth and the oxygen generating compound is increased via the use of a splint or a mouth tray. Illustrative examples of the tray-applied tooth whitening systems include U.S. Pat. Nos. 5,376,006; 5,858,332; 5,764,598; 5,718,886 and 5,171,564
U.S. Pat. No. 5,376,006 discloses splint applied sustained release oral care compositions, which contain a peroxide, a carbomer thickening agent, water and glycerin as a humectant/carrier. These compositions are claimed to be sustained release and require the splint to be worn for greater then two hours.
U.S. Pat. No. 5,858,332 discloses sustained release splint applied oral care compositions which contain a peroxide, a carbomer thickening agent, water, a carboxylic acid peroxide stabilizer and glycerin as a humectant/carrier. These compositions are claimed to be sustained release and require the splint to be worn for greater then two hours.
U.S. Pat. No. 5,746,598 discloses sustained release splint applied oral care compositions which contain a peroxide, a carbomer thickening agent, water, sodium fluoride and glycerin/polyethylene glycol as a humectant/carrier. These compositions are claimed to be sustained release and require the splint to be worn for greater then two hours.
U.S. Pat. No. 5,718,886 discloses splint applied oral care compositions which contain a peroxide, a thickening system consisting of carboxypolymethylene, hydroxypropyl cellulose and xanthan gum. The carriers/humectants are propyleneglycol, polyethyleneglycol, and glycerin.
The drawback with the splint applied compositions described above is that all contain hydrocarbon humectants which may limit the activity of the peroxide ingredient and none contain surface active agents whose absence may prevent solubilization and emulsification of the stain and thus may lead to redeposition of the stain thereby further limiting the bleaching effectiveness of the peroxide.
In contrast to the above, U.S. Pat. No. 5,171,564 discloses an oral care composition which contains an abrasive in combination with a metal free peroxide, a chelating agent, thickening agent such as a polyoxyethylene polypropylene block copolymer and hydrocarbon humectants such as polyethylene glycol, glycerin or sorbitol. This composition is claimed to have utility in brushing applications and splint applied tooth bleaching applications. As in the case above, this composition has a drawback because it contains a hydrocarbon humectant.
Prior art also discloses bleaching gels e.g., U.S. Pat. No. 5,922,307 in which the water content is increased to at least 75% in order to reduce tooth sensitivity and other adverse effects such as demineralization. This patent also teaches the utility of using a calcium chelating agent in order to stabilize the peroxide and enhance the whitening effect. Unfortunately, chelating agents have been shown to increase enamel demineralization in absence of a calcium precipitating agent such as sodium fluoride.
Prior art related to tooth whitening does not mention the possibility of increasing the tooth whitening efficacy by inhibiting the action of catalase. Catalase is an enzyme which has been shown to occur naturally in plague and in saliva. The primary role of catalase is to breakdown hydrogen peroxide into oxygen and water which have a very limited effect on bleaching teeth. Hence, limiting catalase activity would increase the bleaching effect of the peroxide. Prior art concerning bleaching of cellulose paper fibers (U.S. Pat. No. 5,885,412) addresses the issue of premature breakdown and teaches that catalase inhibitors prevent breakdown of peroxide, thus requiring less peroxide for bleaching purposes. The inhibitors of catalase include halogenated compounds such as sodium fluoride, sodium chloride, sodium bromide, hydroxylamine, sulfides and reducing agents such as ascorbic acid. Notably, the catalase inhibiting technology has not been utilized in oral care compositions in order to enhance tooth whitening efficacy.
As indicated above some compositions contain chelating agents. A metal chelating agent can be defined as an agent which sequesters metal ions and renders them unreactive. Generally, there are two types of metal chelating agents. These are: 1) agents such as EDTA, citric acid, alkali metal pyrophospates, phosphonates etc., which combine with metal ions and keep them in solution. These are further divided into two groups; a) organic chelating agents and b) inorganic chelating agents. 2) agents that react with metal ions and cause them to precipitate. An example of this includes fluorides such as sodium fluoride. In prior art concerning non-dental bleaching compositions, chelating agents which keep metal ions in solution have shown to be advantageous because they prevent metal catalyzed breakdown of peroxide. Further, U.S. Pat. No. 6,150,324 teaches the utility of using detergent additives in combination with a mixed metal sequestrant system to obtain improved dishware cleaning compositions. Tooth bleaching prior art does not disclose the benefit of using mixed organic metal chelating agents and condensed phosphate chelating agents in order to obtain compositions which have heightened tooth-whitening abilities. Tooth bleaching prior art also does not disclose the benefit of using metal precipitating chelating agents such as fluorides in order to stabilize the peroxide formulations and also to precipitate calcium compounds onto the tooth surface thus preventing enamel damage. Further, there is contradictory information concerning the utility of metal solubilizing chelating agents in stabilization of peroxide containing dental preparations. U.S. Pat. No. 4,839,156 teaches that chelating agents have adverse effects upon the stability of peroxides. In contrast, U.S. Pat. No. 5,171,564 teaches that chelating agents are essential to the stability of the peroxide preparation. The reason behind this discrepancy is unknown. However, the use of chelating agents that solubilize metal ions offer distinct disadvantages because studies have shown that these agents demineralize and damage enamel surfaces.
Tooth whitening products currently available have additional disadvantages in addition to being slow acting and having adverse effects. These include: poor compliance because compliance in a therapeutic regimen has been shown to be related to the length of the therapy and the frequency of the dosage.
Hence, there is a need for a bleaching product that is safe, rapidly acting and one that fits into the lifestyle of the patient.